Field of the Invention
The present invention relates to a method of use of a scanning probe microscope including the step of cleaning the probe for inspection of a scanning probe microscope in ambient atmosphere, which probe is already processed to have the final shape of a probe. More specifically, the present invention relates to a method of use of a scanning probe microscope including preparation of a probe tip for microscopic inspection such as inspection of atomic image.
A method of cleaning a conductive probe used in a scanning probe microscope (hereinafter referred to as SPM) such as a scanning tunneling microscope (STM) processed to have a shape of a probe by chemical polishing or mechanical processing, and preparing a probe enabling inspection of atomic level has been disclosed, for example, in
(1) Hans-Werner Fink; IBM J. Res. Develop., Vol. 30, No. 5, pp. 460-465 (1986), U. Staufer, L. P. Muray, D. P. Kerns, and T. H. P. Chang; J. Vac. Sci. Technol. B, Vol. 9, No. 6, pp. 2962-2966 (1991), PA1 (2) D. K. Bielgelsen, F. A. Ponce, and J. C. Tramontana; Appl. Phys. Lett., Vol. 50, No. 11, pp. 696-698 (1987), PA1 (3) T. Tiedje, J. Varon, H. Deckman, and J. Strokes; J. Vac. Sci. Technol. A, Vol. 6, No. 2, pp. 372-375 (1998), PA1 (4) M. Tomitori, N. Hirano, F. Iwasaki, Y. Watanabe, T. Takayanagi, and O. Nishikawa; J. Vac. Sci. Technol. A, Vol. 8, No. 1, pp. 425-428 (1990), and PA1 (5) Japanese Patent Laying-Open No. 5-164512.
In the method of preparing a probe disclosed in Article (1), a probe for inspection formed of tungsten (W) is used as a tip of a field ion microscope. (FIM) or a field electron emission microscope (FEEM). Absorbed substance such as organic substance on the surface of tungsten is removed by ions of helium (He), neon (Ne) or argon (Ar), change in the FIM image or the FEEM image caused by disorption or surface diffusion of W atoms at the surface is monitored, and based on the results of monitoring, an optimal probe used for SPM is prepared.
FIG. 14 schematically shows the principal of this method. A high electric field is applied to a probe for inspection and based on an FIM image generated by ions 3 of gas atmosphere such as He or Ne generated at a high potential surface 4, removal of substance absorbed by the surface of the probe 1, disorption of atoms constituting the probe 1 such as W atoms and the state of surface diffusion are monitored. The high electric field is continuously applied until FIM image which corresponds to one atom at the tip of the probe 1 is obtained, and in this manner, cleaning and preparation are performed.
In the method of preparing a probe disclosed in Article (2), ion.milling is used for cleaning and preparation, by which tungsten oxide (WO.sub.x) as an impurity generated at the probe for inspection formed of W is removed.
FIG. 15 schematically shows the principal of this method. Accelerated ions 3 of Ar, for example, are directed obliquely at a prescribed angle .theta. to the tip of the probe 1 for inspection formed of W. The surface 1a of the probe which may be formed by the impurity WO.sub.x is removed by milling, so that the inner portion 1b of the probe is exposed and the tip of the probe 1 is made sharp.
In the method of preparing a probe disclosed in Article (3), nickel (Ni), platinum (Pt) or gold (Au) is provided to cover the probe for inspection formed of platinum (Pt)-iridium (Ir) which has already been processed to have the shape of a probe, by back scattering in which ion collision and sputtering take place simultaneously. In this manner, contamination by an organic substance, for example, is removed.
FIG. 16 schematically shows the principal of this method. Probe 1 for inspection is put in a vacuum chamber 5, and contamination at the tip of probe 1 for inspection is removed by ion collision by an ion beam 8 entering from an ion source 6 through a neutralizer 7 partially neutralizing the ions to the vacuum chamber 5, and at the same time, the tip of probe 1 for inspection is covered by Ni, Pt or Au which is the material of the target electrode 9, by back scattering of atoms constituting the target electrode 9.
In the method of preparing a probe disclosed in Article (4), a probe for inspection formed of Pt--Ir which has already been processed to have the shape of a probe is heated in an ultra high vacuum, and thereafter the tip of the probe is cleaned and prepared by field evaporation.
In the method of preparing a probe disclosed in Article (5), the following components are arranged in a vacuum chamber: a probe for the STM, a sample table movable relative to the probe and allowing positioning of a sample to be measured and a standard sample for evaluating contamination of the probe at portions where tunneling current from the STM probe is provided, and a scanning tunnel microscope body including manipulator means for cleaving the standard sample or a heater. By heating or by applying electric field to the probe, tip of the probe is cleaned, and by measuring tunnel barrier of the probe, whether or not the probe has been cleaned is determined.
However, these conventional methods of cleaning and preparation of the probe for inspection suffers from the following problems.
Namely, in the conventional method, large scale and expensive apparatuses are necessary, such as field ion microscopy, field electron emission microscope, ion milling apparatus, back scattering apparatus and ultra high vacuum apparatus. Further, these conventional methods require troublesome operation of moving the cleaned and prepared probe 1 for inspection to the SPM apparatus.
FIG. 17 is a flow chart showing the conventional method of cleaning and preparation disclosed in Article (1) in which FIM image is used. The flow chart will be briefly described.
First, in a vacuum chamber including FIM apparatus, an SPM probe is mounted (S41).
Thereafter, the vacuum chamber is exhausted to a back ground pressure (generally 10.sup.-10, Pa) allowing FIM measurement (S42).
Inert gas such as He, Ne or the like is introduced and a high electric field is applied to the probe (S43), and the FIM image is monitored (S44).
Application of the voltage is continued until absorbed substance is removed from the surface of the probe by electric field evaporation and an FIM image corresponding to such a state in that only one atom exists at the probe tip is obtained (S45) (the probe tip in this state will be hereinafter referred to as a mono-atomic tip).
When it is determined that the probe tip has become a mono-atomic tip, the vacuum chamber is purged (S46).
The probe is removed from the vacuum chamber and attached to a scanning probe microscope (S47). Scanning (drawing) on a surface of the standard sample is performed (S48), the state of preparation of the probe tip is determined based on the obtained drawn pattern (S49), and if preparation is not sufficient, the same steps from the mounting of probe to the vacuum chamber are repeated (S50).
If preparation is satisfactory, the standard sample is replaced by the sample to be measured (S51), and drawing and processing are performed (S52).
As described above, the conventional methods require large scale vacuum apparatus, and in addition, time necessary for preparation is long. Further, in the conventional methods, the probe is not directly checked by the SPM image itself, but indirectly checked based on the FIM image or the like. Therefore, precise and sure cleaning and preparation were difficult.